6 people can paint 5 walls in 50 minutes. How many minutes will it take for 9 people to paint 6 walls? Round to the nearest minute.
We know the following about the number of walls $w$ painted by $p$ people in $t$ minutes at a constant rate $r$ $w = r \cdot t \cdot p$ $\begin{align*}w &= 5\text{ walls}\\ p &= 6\text{ people}\\ t &= 50\text{ minutes}\end{align*}$ Substituting known values and solving for $r$ $r = \dfrac{w}{t \cdot p}= \dfrac{5}{50 \cdot 6} = \dfrac{1}{60}\text{ walls painted per minute per person}$ We can now calculate the amount of time to paint 6 walls with 9 people. $t = \dfrac{w}{r \cdot p} = \dfrac{6}{\dfrac{1}{60} \cdot 9} = \dfrac{6}{\dfrac{3}{20}} = 40\text{ minutes}$